Processes of this type are known from DE-A-3, 843, 359 and DE-A-3, 643, 359 in which the air of the blowing turbine is cooled by heat exchange with an oxygen-enriched gas stream.
SU-A-739, 316 and SU-A-1, 231, 343 disclose cooling the air coming from a blowing turbine with a stream of nitrogen withdrawn from the medium-pressure column.
In "Proceedings of the British Cryogenics Council Conference, Nov. 13-15 1973" it is proposed to cool the blown air with a stream of residual gas coming from the low-pressure column.
EP-A-0, 081 473 suggests cooling the air expanded in the blowing turbine by heat exchange with a stream of air intended for the medium-pressure column.
EP-A-153, 673 describes an apparatus in which the stream of blown air is cooled by exchanging heat with the nitrogen from the top of the low-pressure column.
FR-A-1, 289, 009 describes cooling the blown air against a stream of pumped liquid oxygen.
EP-A-0, 556, 516 describes cooling the blown air against a rich liquid.
It is frequently necessary to warm a liquid stream coming from the column, for example so as to vaporize it (see EP-A-640, 802).
Thus, it has been proposed to vaporize a purge stream from the collector condenser in the main exchanger of the apparatus, but this requires manufacturing a main exchanger with an additional passage.
EP-A-605, 262 proposes vaporizing the liquid oxygen purges under pressure in order to avoid the risk of a hydrocarbon explosion.